Vulnerability-Lookup

CVE-2026-73491 (GCVE-0-2026-73491)

Vulnerability from cvelistv5 – Published: 2026-08-12 20:59 – Updated: 2026-08-13 13:49

Title

Loofah `allowed_uri?` does not detect `javascript:` URIs split by named whitespace character references

Summary

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.2, Loofah::HTML5::Scrub.allowed_uri? does not reject javascript: URIs whose scheme is split or prefixed with the HTML5 named whitespace character references &Tab; or &NewLine;. CGI.unescapeHTML leaves those references intact, so allowed_uri? reports the URL safe even though a browser decodes and strips the tab or line feed and executes the resulting javascript: URL. This issue affects only callers that pass HTML-encoded strings directly to allowed_uri?; Loofah's default sanitize() path is not affected. This issue is fixed in version 2.25.2.

Severity

2.3 (Low)


                        
                          CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-13 13:49 UTC

CWE

CWE-184 - Incomplete List of Disallowed Inputs

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/flavorjones/loofah/security/ad…	x_refsource_CONFIRM
https://github.com/flavorjones/loofah/pull/308	x_refsource_MISC
https://github.com/flavorjones/loofah/commit/5e91…	x_refsource_MISC
https://github.com/flavorjones/loofah/releases/ta…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
flavorjones	loofah	Affected: >= 2.25.0, < 2.25.2	guessed

Show details on NVD website

JSON

To clipboard

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}

FKIE_CVE-2026-73491

Vulnerability from fkie_nvd - Published: 2026-08-12 21:17 - Updated: 2026-09-09 20:58

Severity

2.3 (Low) - CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/flavorjones/loofah/commit/5e91af861e3cdab47b91dd0b81f3afdfd13a5e19
	security-advisories@github.com	https://github.com/flavorjones/loofah/pull/308
	security-advisories@github.com	https://github.com/flavorjones/loofah/releases/tag/v2.25.2
	security-advisories@github.com	https://github.com/flavorjones/loofah/security/advisories/GHSA-8whx-365g-h9vv

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "loofah",
          "vendor": "flavorjones",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 2.25.0, \u003c 2.25.2"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
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    {
      "lang": "en",
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    }
  ],
  "id": "CVE-2026-73491",
  "lastModified": "2026-09-09T20:58:37.713",
  "metrics": {
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      {
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          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
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          "exploitMaturity": "NOT_DEFINED",
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          "modifiedPrivilegesRequired": "NOT_DEFINED",
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    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/flavorjones/loofah/releases/tag/v2.25.2"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/flavorjones/loofah/security/advisories/GHSA-8whx-365g-h9vv"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-184"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-8WHX-365G-H9VV

Vulnerability from github – Published: 2026-07-21 15:04 – Updated: 2026-08-12 20:59

Summary

Loofah `allowed_uri?` does not detect `javascript:` URIs split by named whitespace character references

Details

Summary

Loofah::HTML5::Scrub.allowed_uri? does not correctly reject javascript: URIs when the scheme is split or prefixed by the HTML5 named character references &Tab; (tab) or &NewLine; (line feed).

This is a bypass of the fix for GHSA-46fp-8f5p-pf2m, which handled the equivalent numeric character references (	, 
, ) but did not cover the named forms.

Details

allowed_uri? decodes HTML entities with CGI.unescapeHTML, which handles numeric character references but not HTML5 named character references. Payloads like java&Tab;script:alert(1) are therefore left intact, so the method does not recognize the javascript: scheme and returns true. A browser, however, decodes &Tab; and &NewLine; to tab and line feed and strips them from the URL during parsing, producing javascript:alert(1).

&Tab; and &NewLine; are the only relevant named character references: across the HTML5 named-character table, they are the only two that decode to characters the WHATWG URL parser strips from a URL (U+0009 and U+000A; there is no named reference for U+000D).   / &NonBreakingSpace; decode to U+00A0, which browsers do not strip, so they aren't usable for this bypass.

Note that Loofah's default sanitize() path is not affected, because Nokogiri decodes or entity-escapes HTML entities during parsing before Loofah evaluates the URI protocol. This issue only affects callers of the public allowed_uri? string-level helper that pass it HTML-encoded strings.

Impact

Callers that validate a user-controlled URL with Loofah::HTML5::Scrub.allowed_uri? and then render the approved value into an href or other browser-interpreted URI attribute may be vulnerable to cross-site scripting (XSS). This includes applications that call allowed_uri? directly, as well as higher-level features built on top of it, such as Action Text 8.2's markdown link validation.

Mitigation

Upgrade to Loofah >= 2.25.2.

Credit

Responsibly reported by GitHub user @connorshea.

Severity

2.3 (Low)


                  
                    CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "loofah"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.25.0"
            },
            {
              "fixed": "2.25.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-73491"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-184"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-21T15:04:14Z",
    "nvd_published_at": null,
    "severity": "LOW"
  },
  "details": "## Summary\n\n`Loofah::HTML5::Scrub.allowed_uri?` does not correctly reject `javascript:` URIs when the scheme is split or prefixed by the HTML5 named character references `\u0026Tab;` (tab) or `\u0026NewLine;` (line feed).\n\nThis is a bypass of the fix for [GHSA-46fp-8f5p-pf2m](https://github.com/flavorjones/loofah/security/advisories/GHSA-46fp-8f5p-pf2m), which handled the equivalent numeric character references (`\u0026#9;`, `\u0026#10;`, `\u0026#13;`) but did not cover the named forms.\n\n## Details\n\n`allowed_uri?` decodes HTML entities with `CGI.unescapeHTML`, which handles numeric character references but not HTML5 named character references. Payloads like `java\u0026Tab;script:alert(1)` are therefore left intact, so the method does not recognize the `javascript:` scheme and returns `true`. A browser, however, decodes `\u0026Tab;` and `\u0026NewLine;` to tab and line feed and strips them from the URL during parsing, producing `javascript:alert(1)`.\n\n`\u0026Tab;` and `\u0026NewLine;` are the only relevant named character references: across the HTML5 named-character table, they are the only two that decode to characters the WHATWG URL parser strips from a URL (U+0009 and U+000A; there is no named reference for U+000D). `\u0026nbsp;` / `\u0026NonBreakingSpace;` decode to U+00A0, which browsers do not strip, so they aren\u0027t usable for this bypass.\n\nNote that Loofah\u0027s default `sanitize()` path is **not** affected, because Nokogiri decodes or entity-escapes HTML entities during parsing before Loofah evaluates the URI protocol. This issue only affects callers of the public `allowed_uri?` string-level helper that pass it HTML-encoded strings.\n\n## Impact\n\nCallers that validate a user-controlled URL with `Loofah::HTML5::Scrub.allowed_uri?` and then render the approved value into an `href` or other browser-interpreted URI attribute may be vulnerable to cross-site scripting (XSS). This includes applications that call `allowed_uri?` directly, as well as higher-level features built on top of it, such as Action Text 8.2\u0027s markdown link validation.\n\n## Mitigation\n\nUpgrade to Loofah \u003e= 2.25.2.\n\n## Credit\n\nResponsibly reported by GitHub user @connorshea.",
  "id": "GHSA-8whx-365g-h9vv",
  "modified": "2026-08-12T20:59:24Z",
  "published": "2026-07-21T15:04:14Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/flavorjones/loofah/security/advisories/GHSA-8whx-365g-h9vv"
    },
    {
      "type": "WEB",
      "url": "https://github.com/flavorjones/loofah/commit/5e91af861e3cdab47b91dd0b81f3afdfd13a5e19"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/flavorjones/loofah"
    },
    {
      "type": "WEB",
      "url": "https://github.com/flavorjones/loofah/releases/tag/v2.25.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Loofah `allowed_uri?` does not detect `javascript:` URIs split by named whitespace character references"
}

UBUNTU-CVE-2026-73491 (CVE-2026-73491)

Vulnerability from osv_ubuntu – Published: 2026-08-12 21:17 – Updated: 2026-08-19 11:11 – Source website

Details

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.2, Loofah::HTML5::Scrub.allowed_uri? does not reject javascript: URIs whose scheme is split or prefixed with the HTML5 named whitespace character references or . CGI.unescapeHTML leaves those references intact, so allowed_uri? reports the URL safe even though a browser decodes and strips the tab or line feed and executes the resulting javascript: URL. This issue affects only callers that pass HTML-encoded strings directly to allowed_uri?; Loofah's default sanitize() path is not affected. This issue is fixed in version 2.25.2.

Severity

2.3 (Low)


                    
                      CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

N/A (UNKNOWN)


                    
                      medium

References

URL

Type

	https://ubuntu.com/security/CVE-2026-73491	REPORT
	https://www.cve.org/CVERecord?id=CVE-2026-73491	REPORT
	https://github.com/flavorjones/loofah/security/ad…	REPORT
	https://github.com/flavorjones/loofah/pull/308	REPORT
	https://github.com/flavorjones/loofah/commit/5e91…	REPORT
	https://github.com/flavorjones/loofah/releases/ta…	REPORT

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "ruby-loofah",
            "binary_version": "2.0.3-2+deb9u3build0.16.04.1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:16.04:LTS",
        "name": "ruby-loofah",
        "purl": "pkg:deb/ubuntu/ruby-loofah@2.0.3-2+deb9u3build0.16.04.1?arch=source\u0026distro=xenial"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.0.2-1",
        "2.0.3-1",
        "2.0.3-2",
        "2.0.3-2+deb9u1build0.16.04.1",
        "2.0.3-2+deb9u2build0.16.04.1",
        "2.0.3-2+deb9u3build0.16.04.1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "ruby-loofah",
            "binary_version": "2.2.2-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:18.04:LTS",
        "name": "ruby-loofah",
        "purl": "pkg:deb/ubuntu/ruby-loofah@2.2.2-1?arch=source\u0026distro=bionic"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.0.3-2",
        "2.2.2-1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "ruby-loofah",
            "binary_version": "2.4.0+dfsg-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:20.04:LTS",
        "name": "ruby-loofah",
        "purl": "pkg:deb/ubuntu/ruby-loofah@2.4.0+dfsg-1?arch=source\u0026distro=focal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.2.3-1",
        "2.3.1+dfsg-1",
        "2.4.0+dfsg-1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "ruby-loofah",
            "binary_version": "2.13.0-2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:22.04:LTS",
        "name": "ruby-loofah",
        "purl": "pkg:deb/ubuntu/ruby-loofah@2.13.0-2?arch=source\u0026distro=jammy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.12.0-1",
        "2.13.0-1",
        "2.13.0-2"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "ruby-loofah",
            "binary_version": "2.22.0-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:24.04:LTS",
        "name": "ruby-loofah",
        "purl": "pkg:deb/ubuntu/ruby-loofah@2.22.0-1?arch=source\u0026distro=noble"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.21.3-1",
        "2.21.4-1",
        "2.22.0-1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "ruby-loofah",
            "binary_version": "2.25.0-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:26.04:LTS",
        "name": "ruby-loofah",
        "purl": "pkg:deb/ubuntu/ruby-loofah@2.25.0-1?arch=source\u0026distro=resolute"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.24.1-1",
        "2.25.0-1"
      ]
    }
  ],
  "aliases": [],
  "details": "Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.2, Loofah::HTML5::Scrub.allowed_uri? does not reject javascript: URIs whose scheme is split or prefixed with the HTML5 named whitespace character references \u0026Tab; or \u0026NewLine;. CGI.unescapeHTML leaves those references intact, so allowed_uri? reports the URL safe even though a browser decodes and strips the tab or line feed and executes the resulting javascript: URL. This issue affects only callers that pass HTML-encoded strings directly to allowed_uri?; Loofah\u0027s default sanitize() path is not affected. This issue is fixed in version 2.25.2.",
  "id": "UBUNTU-CVE-2026-73491",
  "modified": "2026-08-19T11:11:14Z",
  "published": "2026-08-12T21:17:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2026-73491"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-73491"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/flavorjones/loofah/security/advisories/GHSA-8whx-365g-h9vv"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/flavorjones/loofah/pull/308"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/flavorjones/loofah/commit/5e91af861e3cdab47b91dd0b81f3afdfd13a5e19"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/flavorjones/loofah/releases/tag/v2.25.2"
    }
  ],
  "related": [],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N",
      "type": "CVSS_V4"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2026-73491"
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-73491 (GCVE-0-2026-73491)

FKIE_CVE-2026-73491

GHSA-8WHX-365G-H9VV

Summary

Details

Impact

Mitigation

Credit

UBUNTU-CVE-2026-73491 (CVE-2026-73491)

Tags

Sightings

Nomenclature

Related by attack behaviour